Method of manufacturing elongate members and workpiece therefor

ABSTRACT

A method of forming an elongate composite product wherein a composite body formed of an internal billet and an external sleeve is assembled, the interior periphery of the sleeve being complimentary to the exterior periphery of the billet, the composite body then being formed as by extruding into an elongate product having an inner core and an outer sheath.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the manufacture of composite elongate members and, more particularly, to the manufacture of extruded elongate composite members.

2. Description of Prior Art

U.S. Pat. No. 6,350,327 discloses a method of manufacturing clad pipes wherein a cladding material is metallurgically bonded to the hollow body of base material, the composite body being extruded to form the pipe.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention there is provided a method of forming a composite elongate product. According to this aspect of the invention, a billet, which can be solid or tubular is formed by a suitable technique. A sleeve is also formed by a suitable technique. The billet has an outer peripheral surface while the sleeve has an inner peripheral surface. The inner and outer peripheral surfaces of the sleeve and billet, respectively, are complimentary to one another. A composite body can be formed by shrink fitting the billet in the sleeve or the billet can be snugly received, e.g., press fitted in the sleeve. End caps can be attached to the sleeve at each end thereby encasing the billet in the sleeve. Alternatively, both shrink fitting or press fitting and the use of end caps can be employed to form the composite body. Once the composite body is formed, it is then subjected to forming by a suitable metal working technique, e.g., extrusion, to elongate the composite body into an elongate composite product having a core and an outer sheath.

Another aspect of the present invention provides a workpiece for forming a composite, elongated product. The workpiece is comprised of a billet received in a sleeve. The outer peripheral surface of the billet and the inner peripheral surface of the sleeve are complimentary to one another, the billet being generally snugly received in the sleeve. The billet can be shrink fitted or press fitted into the sleeve. End caps can be attached to the sleeve at each end to thereby encase the billet in the sleeve and the end caps. In either case there is formed a composite body which can be subjected to forming by various metal working techniques, e.g., extrusion, to form an elongate, composite product. In another embodiment, both shrink fitting and the use of end caps can be employed to form the composite body.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view, in section, of a workpiece according to one aspect of the present invention.

FIG. 2 is a side elevational view, in section, of an elongated composite product made from the workpiece of FIG. 1.

FIG. 3 is a side elevational view, in section, of another workpiece according to another aspect of the present invention.

FIG. 4 is a side elevational view, in section, of an elongated, composite product made from the workpiece of FIG. 3; and

FIG. 5 is a flow diagram depicting one method of forming elongated, composite products according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring first to FIG. 1 there is shown a workpiece 10 comprised of a billet 12, a sleeve 14 and first and second end caps 16 and 18. Core 12 is of metallic construction and has a first end 20 and a second end 22. As shown, billet 12 is cylindrical when viewed in transverse cross section and has an outer peripheral surface 24 which is generally cylindrical. Metallic sleeve 14 has a first end 26 and a second end 28. Sleeve 14 has an inner peripheral surface 30 which is complimentary to surface 24, i.e., it is cylindrical in shape and, as seen, surfaces 24 and 30 are complimentary to one another and sized so as to be closely adjacent and indeed preferably in engagement with one another. First end cap 16 has a body portion 16A and a neck portion 16B both of which are cylindrical when viewed in transverse cross section, neck portion 16B having an outer peripheral surface 16C which generally conforms to inner peripheral surface 30 of sleeve 14. As seen, cap 16 is connected to sleeve 14 by means of a weld 31. Cap 18 is generally in the shape of a disc and is attached to the end 28 of sleeve 14 by weld 32. Thus, billet 12 is essentially encased in the cylindrical chamber formed by sleeve 14 and end caps 16 and 18. In addition to the use of end caps 16 and 18, the composite workpiece 10 can also advantageously be made by shrink fitting billet 12 in sleeve 14. Alternatively, end caps 16 and 18 can be dispensed with in lieu of simply shrink fitting billet 12 in sleeve 14. For most applications, it has been found desirable to use both shrink fitting and end caps 16 and 18 to form the workpiece 10.

To assemble workpiece 10, billet 12 and sleeve 14 would be separately formed, billet 12 being then inserted into sleeve 14 or, stated differently, sleeve 14 being slid over billet 12. In cases where billet 12 was shrink fitted in sleeve 14, and as well understood by those skilled in the art, sleeve 14 would be heated sufficiently so as to allow it to expand whereupon billet 12 would be inserted and the assembly cooled. In manufacturing sleeve 14 and billet 12, the OD of billet 12 and the ID of sleeve 14 will preferably be machined so that there is a close fit even in the absence of heat shrinking. While as shown, billet 12, sleeve 14 and end caps 16 and 18 are all cylindrical when viewed in transverse cross section, it will be appreciated that other cross-sectional configurations, e.g., polygonal, could be employed.

Turning now to FIG. 2, there is shown an elongated, composite product obtained by extruding workpiece 10 as described hereafter. As can be seen in FIG. 2, composite product 34 has a core 36 formed from billet 12 and a sheath 38 formed from sleeve 14, end caps 16 and 18 having been removed. The elongated, composite product formed by extruding the workpiece 10 of FIG. 1, is as shown in FIG. 2, a solid body, the extrusion process forming a bond between core 36 and sheath 38.

Turning now to FIG. 3 there is shown another workpiece that can be used for manufacturing a tubular elongate composite product. Workpiece 40 shown in FIG. 3 comprises a tubular billet 42 having a bore 44 therethrough, billet or tubular member 42 being received in a sleeve 46, the workpiece 40 being provided with end caps 48 and 50 having bores 49 and 51, respectively. As is the case with the workpiece shown in FIG. 1, the workpiece shown in FIG. 3 is cylindrical and the sizing of tubular member or billet 42 and sleeve 46 as well as the shape thereof are as described above with respect to the workpiece 10 shown in FIG. 3, i.e., tubular member 42 will generally fit snugly into sleeve 46.

As described above with respect to workpiece 10, workpiece 40 can be formed without end caps 48 and 50 and in that event, generally billet 42 would be heat shrink fitted into sleeve 46. Again, as described above with respect to workpiece 10, preferably workpiece 40 is formed with end caps 48 and 50 and with billet 42 being heat shrink fitted into sleeve 46.

The elongated composite product 52 produced by extruding workpiece 40 is shown in FIG. 4, product 52 comprising a core 54 formed from billet 42 and having a bore 58 therethrough, and an outer sheath 56 formed from sleeve 46, end caps 48 and 50 having been removed.

The billet and the sleeve, as noted above, are both of metallic construction albeit that they are different metals. A wide variety of materials can be used for the billet and the sleeve. For example, if it is desired that the composite product have an outer surface which is corrosion resistant, then the workpiece could be formed from a billet of corrosion prone material while the sleeve was formed of a corrosion resistant material. By way of example only, the billet could be formed of carbon steel while the sleeve was formed of INCONEL, e.g., INCONEL 625. Indeed, the construction of the elongate product can be tailored to meet a wide variety of applications. In cases where the elongate product were in the form of a tubular member such is shown in FIG. 4 and it was desired that the tubular member carry corrosive fluids, then the billet could be made from a corrosion resistant material while the sleeve could be made from a corrosion prone material. In making such a corrosion resistant tubular member for carrying corrosive fluids, the radial thickness of the billet which formed the core of the tubular member could be reduced to the point such that only a relatively thin liner of corrosion resistant material formed from the billet would remain after the extrusion process. To give the tubular member required structural integrity, the sleeve of the workpiece used to form the tubular member could be of a greater radial thickness albeit that it was made of a corrosion prone and thus cheaper material. Thus, for example, the core of the elongated product of a typical tubular member could comprise titanium and the sheath carbon steel or some other less expensive and more corrosion prone material.

As noted above, the composite workpiece from which the extruded product is made can be constructed in several ways. For example, the billet and the sleeve can have there outer surfaces and inner surfaces, respectively, machined such that there is a close, snug fit, e.g., press fit, between the billet and the sleeve when the former is received in the latter. With this close fit, end caps can then be attached to each end of the sleeve and the workpiece extruded to achieve the elongated product. In this above-described method, although there would be a close fit between the billet and the sleeve, the billet would not be shrink fitted into the sleeve. In a second manner of making the workpiece, the end caps could be dispensed with and the billet and sleeve shrink fitted together following which the assembled workpiece would be extruded. A less desirable variation of this method would be to closely machine the outer surface of the billet and the inner surface of the sleeve such that when they were fitted together there was snug engagement between the inner peripheral surface of the sleeve and the outer peripheral surface of the billet. Lastly, and in most cases, the use of end caps and shrink fitting is employed as this provides an elongated product in which the bonding between the core and the sheath is enhanced and there is minimal waste of material.

The term “bonded” as used herein with respect to the engagement between the core and the sheath of the extruded product, is intended to mean that the core and the sheath are in such tight engagement that they are for all intents and purposes inseparable. While a metallurgical bond between the core and the sheath may indeed be formed, it is certainly believed that a mechanical bond between those components is formed.

The end caps serve important purposes when they are employed. With respect to the first end cap or the end cap moving in the direction of the extrusion, it holds the billet in position in the sleeve and forces the sleeve to start elongating before the billet starts elongating. Without the first end cap, it is possible that the sleeve would stay stationary and the billet would be forced out from the end of the sleeve in the direction of the extrusion. Thus there would be significant waste of material. The second end cap serves the purpose of displacing material so that the yield on the extrusion can be maximized. In effect, since the second end cap can be made of a relatively cheap material, e.g., carbon steel, more of the billet and sleeve can be extruded towards the end of the extrusion stroke thereby maximizing yield.

In the description above, reference has been made to extrusion. As is well known, extrusion is a method of forging just as rolling is a form of forging. As is well know to those in the art, there are various types of forging processes. For example, in extrusion, the workpiece is placed in a container and compressed until pressure inside the metal reaches flow stress levels and the workpiece generally completely fills the container. Additional pressure causes it to travel through an orifice and form the extruded (elongated) product.

In forming the elongated product of the present invention, the workpieces can be extruded at temperatures ranging from 1300 to 2200° F. It will be understood that the temperature in the extrusion process or other forging process, will depend upon the material makeup of the billet and the sleeve.

As noted above, when the elongated product has been formed, the end caps are removed. In this regard it should be noted that the first end cap, i.e., the end cap on the leading end of the extrusion, in addition to the purpose described above regarding preventing the billet from flowing before the sleeve flows also serves an important function of minimizing material loss. For example, without the addition of the first end cap, because the initial extrusion would not be steady state between the two components, i.e., the billet and the sleeve, a significant portion of the initially extruded product would have to be discarded. However, by using the end caps the amount of material wasted is greatly minimized since steady state extrusion between the two components occurs from the beginning to the end of the extrusion process.

Reference is now made to FIG. 5 for a description of one embodiment of the method of the present invention. In forming the workpiece, there is an inner material or billet and an outer material or sleeve. Turning first to formation of the billet or inner material, in step B1 the billet is formed by a suitable method depending upon whether it is a solid piece or a tubular member. Once formed, in step B2 the billet is machined and in this regard the OD or peripheral surface is machined to a desired surface finish and dimension. For example, if the billet is cylindrical it can be machined so that the OD is of the desired dimension and within predetermined tolerances. In step B3, the machined billet is inspected to determine the surface characteristics and dimensions.

Turning to the formation of the sleeve, since it is tubular in nature, it is formed in any suitable method to obtain a tubular member having generally the desired ID and OD, again assuming that the sleeve is cylindrical. In step S2, the sleeve is machined, if necessary, primarily on its inner peripheral surface.

The billet and sleeve, having been formed and inspected are then assembled by one of the techniques described above. For example, in step 100 a billet can be heat shrink fitted into the sleeve or the billet and the sleeve, because of their close matching dimensions and tolerances can be fitted together in what might be considered a press fit. The assembly of the composite body comprising the billet and the sleeve is then inspected in step 102. Following inspection, and in step 104, end caps can be optionally attached to the sleeve, e.g., by tack welding, a continuous weld or the like. Following the attachment of the end caps, if that step is conducted, the entire assembly is heated in step 106 to the desired metalworking temperature, again depending upon the nature of the metals forming the billet and the sleeve. Heating can be conducted in a variety of fashions well known to those in the metalworking art. When the composite assembly of billet, sleeve and optionally end caps is heated to the desired temperature, it is then forged, e.g., extruded in step 108 to form the elongate product. Optionally, in step 110 and if required, the elongate product can be heat treated. Following heat treating, if employed, the elongate product is subjected in step 112 to mechanical testing to determine various physical characteristics. In step 114, the OD of the elongate product is then checked and machined if desired to obtain the desired OD. Following step 114, non-destructive testing is conducted on the elongate product at step 116 followed by a final inspection in step 118. Step 118 may include, for example, radiography, ultrasonic, eddy current, etc., to determine, to the extent possible, the physical structure and characteristics of the elongated product.

The elongate product produced by the method of the present invention, as noted above, can be used to form tubular members having a cladding on the ID which is corrosion resistant and a sheath surrounding the cladding which is of a less expensive material but which provides the necessary structural integrity.

In terms of final use products from which the elongate products produced by the method of the present invention can be used, in hydraulic piston/cylinder combinations, the piston rods are quite often subject to corrosive attack. Using the method of the present invention, solid piston rods could be made wherein the core was made of a corrosion prone material but the sheath was of a corrosion resistant material. Thus, the rods could be produced without the necessity for expensive plating, coating or welding techniques.

In the preferred method of the present invention employing both the use of end caps along with shrink fitting, there is much less waste of material since the end caps provide maximum coextrusion of the billet and sleeve while the shrink fitting helps to ensure a strong mechanical, if not a metallurgical bond, during the extrusion process.

The foregoing description and examples illustrate selected embodiments of the present invention. In light thereof, variations and modifications will be suggested to one skilled in the art, all of which are in the spirit and purview of this invention. 

1. A method of forming an elongate composite product comprising: forming a billet of a first metallic material, said billet having an outer peripheral surface; forming a sleeve of a second metallic material, said sleeve having an inner peripheral surface, said inner and outer peripheral surfaces being complimentary to one another; shrink fitting said billet in said sleeve to form a composite body; and forming said composite body into an elongate product.
 2. The method of claim 1, wherein said billet comprises a tubular member.
 3. The method of claim 1, wherein said billet comprises a solid member.
 4. The method of claim 2, wherein said tubular member comprises a corrosion prone material.
 5. The method of claim 4, wherein said sleeve comprises a corrosion resistant material.
 6. The method of claim 3, wherein said billet comprises a corrosion prone material.
 7. The method of claim 6, wherein said sleeve comprises a corrosion resistant material.
 8. The method of claim 1, wherein said sleeve has a first end and a second end and further comprising: securing a first end cap to said sleeve on said first end; securing a second end cap to said sleeve on said second end, said billet being confined by said sleeve and said first and second end caps to form a composite body.
 9. The method of claim 8, wherein said first and second caps are attached to said sleeve by welding.
 10. The method of claim 8, comprising removing said first and second end caps from said elongate product.
 11. A method of forming an elongate composite product comprising: forming a billet of a first metallic material, said billet having an outer peripheral surface; forming a sleeve of a second metallic material, said sleeve having a first end, a second end and an inner peripheral surface, said inner and outer peripheral surfaces being complimentary to one another; and positioning said sleeve over said billet; securing a first end cap to said sleeve on said first end; securing a second end cap to said sleeve on said second end, said billet being confined by said sleeve and said first and second end caps to form a composite body; and forming said composite body into an elongate product.
 12. The method of claim 11, wherein said billet comprises a tubular member.
 13. The method of claim 11, wherein said billet comprises a solid member.
 14. The method of claim 11, wherein said first and second ends are attached to said sleeve by welding.
 15. The method of claim 8, comprising removing said first and second end caps from said elongate product.
 16. The method of claim 11, comprising shrink fitting said billet in said sleeve.
 17. A workpiece for forming into an elongate product comprising: a billet having an outer surface; a sleeve having a first end and second end and an inner surface, said inner surface conforming to said outer surface, said billet being received in said sleeve; a first end cap attached to said first end of said sleeve; and a second end cap attached to said second end of said sleeve.
 18. The workpiece of claim 17, wherein said first and second end caps are attached by welding.
 19. The workpiece of claim 17, wherein said first cap comprises a body portion and a neck portion, said neck portion having a peripheral outer surface conforming to said inner surface, said neck portion being received in said first end of said sleeve.
 20. The workpiece of claim 17, wherein said billet comprises a solid member.
 21. The workpiece of claim 17, wherein said billet comprises a tubular member.
 22. The workpiece of claim 20, wherein said sleeve comprises a corrosion resistant material.
 23. The workpiece of claim 20, wherein said billet comprises a corrosion prone material.
 24. The workpiece of claim 21, wherein said tubular member comprises a corrosion prone material.
 25. The workpiece of claim 22, wherein said sleeve comprises a corrosion resistant material.
 26. The workpiece of claim 13, wherein said first and second end caps have a peripherally extending outer surface conforming to said outer surface of said sleeve.
 27. The workpiece of claim 17, wherein said billet is shrink fitted in said sleeve.
 28. A workpiece for forming into an elongate product comprising: a billet having an outer surface; a sleeve having a first end and second end and an inner surface, said inner surface conforming to said outer surface, said billet being shrink fitted in said sleeve.
 29. The workpiece of claim 28, wherein said billet comprises a solid member.
 30. The workpiece of claim 28, wherein said billet comprises a tubular member.
 31. The workpiece of claim 29, wherein said sleeve comprises a corrosion resistant material.
 32. The workpiece of claim 31, wherein said billet comprises a corrosion prone material.
 33. The workpiece of claim 30, wherein said tubular member comprises a corrosion prone material.
 34. The workpiece of claim 33, wherein said sleeve comprises a corrosion resistant material.
 35. The workpiece of claim 28, wherein said sleeve has first and second ends and, a first end cap being attached to said first end, a second end cap being attached to said second end.
 36. The workpiece of claim 35, wherein said first and second end caps have a peripherally extending outer surface conforming to said outer surface of said sleeve.
 37. The workpiece of claim 35, wherein said first end cap has a body portion and a neck portion, said neck portion having an outer peripheral surface conforming to said inner surface, said neck portion being received in said first end of said sleeve.
 38. The method of any of claims 1 or 11, wherein said forming comprises extruding. 